Introduced in xorg-server-1.13.99.901-2-g9ad0fdb1

. Storing the grab pointer
in the listener turns out to be a bad idea. If the grab is not an active
grab or an implicit grab, the pointer stored is the one to the grab attached
on the window. This grab may be removed if the client calls UngrabButton or
similar while the touch is still active, leaving a dangling pointer.

To avoid this, copy the grab wherever we need to reference it later. This
is also what we do for pointer/keyboard grabs, where we copy the grab as
soon as it becomes active.

Reported-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>